I have given this question 23 hours of thought. My answer is leather.

I have a Schott Perfecto purchased used at an army surplus store in 1991. It remains in perfect shape despite being in a crash.

I have a Hein Gericke Dakar, branded Victory Motorcycle Corp, purchased used on eBay for $80 in 2003. It remains in perfect shape despite being in a crash.

Shit, I have a J Crew leather jacket gifted me new in 1995 that, despite being faded, despite being a piece of shit J Crew leather jacket, has been relined twice and remains in excellent shape. For that matter I have a hand-me-down Brooks Brothers nubuck suede leather trenchcoat from the '80s that looks new.

My first pair of Carolina 116s were purchased new for $120 in 1991, resoled twice, and finally discarded after my utter and total lack of care over 20 years caused a crack big enough to push my thumb through. I tried filling it with shoe goo and it made a bump that hurt my toe. My second pair is still on their first soles.

My $7800 leather sectional, which I bought for $1100 one year old in 2002, needs some refinishing but I know I could get the leather filled, get it restuffed and have a brand new couch for about $600.

Leather. Leather, treated well, lasts forever. And the older it gets, the more it's worth.

Unless it's Doc Martens. Docs fall apart in like 4 years. Fuck Doc Martens.